Anodes for lithium-based energy storage devices, and methods for making same

ABSTRACT

An anode for an energy storage device includes a current collector having a metal oxide layer. A continuous porous lithium storage layer overlays the metal oxide layer, and a first supplemental layer overlays the continuous porous lithium storage layer. The continuous porous lithium storage layer may be substantially free of nanostructures. The continuous lithium storage layer may include amorphous silicon deposited by a PECVD process. The first supplemental layer includes silicon nitride, silicon dioxide, or silicon oxynitride. The anode may further include a second supplemental layer overlaying the first supplemental layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.16/991,623, filed Aug. 12, 2020 and claims the benefit of U.S.Provisional Application No. 62/886,177, filed Aug. 13, 2019, both ofwhich are hereby incorporated by reference in their entirety for allpurposes.

TECHNICAL FIELD

The present disclosure relates to lithium ion batteries and relatedenergy storage devices.

BACKGROUND

Silicon has been proposed as a potential material for lithium-ionbatteries to replace the conventional carbon-based anodes which have astorage capacity that is limited to −370 mAh/g. Silicon readily alloyswith lithium and has a much higher theoretical storage capacity (3600 to4200 mAh/g at room temperature) than carbon-based anodes. However,insertion and extraction of lithium into the silicon matrix causessignificant volume expansion (>300%) and contraction. This can result inrapid pulverization of the silicon into small particles and electricaldisconnection from the current collector.

The industry has recently turned its attention to nano- ormicro-structured silicon to reduce the pulverization problem, i.e.,silicon in the form of spaced apart nano- or micro-wires, tubes,pillars, particles and the like. The theory is that making thestructures nano-sized avoids crack propagation and spacing them apartallows more room for volume expansion, thereby enabling the silicon toabsorb lithium with reduced stresses and improved stability compared to,for example, macroscopic layers of bulk silicon.

Despite research into structured silicon approaches, such batteriesbased solely on silicon have yet to make a large market impact due tounresolved problems. A significant issue is the manufacturing complexityand investment required to form these anodes. For example, US20150325852describes silicon made by first growing a silicon-based, non-conformal,porous layer on a nanowire template by plasma-enhanced chemical vapordeposition (PECVD) followed by deposition of a denser, conformal siliconlayer using thermal chemical vapor deposition (CVD). Formation ofsilicon nanowires can be very sensitive to small perturbations indeposition conditions making quality control and reproducibility achallenge. Other methods for forming nano- or micro-structured siliconuse etching of silicon wafers, which is time-consuming and wasteful.Further, the connection between silicon wires to a current collector isinherently fragile and the structures are prone to break or abrade awaywhen subjected to handling stresses needed to manufacture a battery.

SUMMARY

There remains a need for anodes for lithium-based energy storage devicessuch as Li-ion batteries that are easy to manufacture, robust tohandling, high in charge capacity and amenable to fast charging, forexample, at least 1 C. These and other needs are addressed by theembodiments described herein.

In accordance with an embodiment of this disclosure, an anode for anenergy storage device is provided that includes a current collectorhaving a metal oxide layer. A continuous porous lithium storage layeroverlays the metal oxide layer, and a first supplemental layer overlaysthe continuous porous lithium storage layer. The first supplementallayer includes silicon nitride, silicon dioxide, or silicon oxynitride.

In accordance with another embodiment of this disclosure, an anode foran energy storage device is provided that includes a current collectorhaving a metal oxide layer, a continuous porous lithium storage layeroverlaying the metal oxide layer, a first supplemental layer overlayingthe continuous porous lithium storage layer, and a second supplementallayer overlaying the first supplemental layer. The first supplementallayer includes silicon nitride, silicon dioxide, silicon oxynitride, ora first metal compound. The second supplemental layer characterized by acomposition different than the first supplemental layer composition, andincludes silicon dioxide, silicon nitride, silicon oxynitride, or asecond metal compound. One of the first supplemental layer or the secondsupplemental layer includes titanium dioxide and has a thickness in arange of about 2 nm to about 50 nm.

The present disclosure provides anodes for energy storage devices thatmay have one or more of at least the following advantages relative toconventional anodes: improved stability at aggressive ≥1 C chargingrates; higher overall areal charge capacity; higher charge capacity pergram of silicon; improved physical durability; simplified manufacturingprocess; and more reproducible manufacturing process.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of an anode according to someembodiments of the present disclosure.

FIG. 2 is a cross-sectional view of a prior art anode.

FIG. 3 is a cross-sectional view of an anode according to someembodiments of the present disclosure.

FIG. 4 is a cross-sectional view of an anode according to someembodiments of the present disclosure.

FIG. 5 is a cross-sectional view of an anode according to someembodiments of the present disclosure.

FIG. 6 is a cross-sectional view of an anode according to someembodiments of the present disclosure.

FIG. 7A is a cross-sectional view of an anode according to someembodiments of the present disclosure.

FIG. 7B is a cross-sectional view of an anode according to someembodiments of the present disclosure.

FIG. 8 is a process flow diagram for preparing anodes according tocertain embodiments of the present disclosure.

FIG. 9A is a schematic of apparatuses for roll-to-roll processing ofanodes according to some embodiments of the present disclosure.

FIG. 9B is a schematic of apparatuses for roll-to-roll processing ofanodes according to some embodiments of the present disclosure.

FIG. 10 is a cross-sectional view of a battery according to someembodiments of the present disclosure.

FIG. 11 show cycling performance data for anodes according to someembodiments of the present disclosure.

FIG. 12 show cycling performance data for anodes according to someembodiments of the present disclosure.

FIG. 13 show cycling performance data for anodes according to someembodiments of the present disclosure.

FIG. 14 show cycling performance data for anodes according to someembodiments of the present disclosure.

DETAILED DESCRIPTION

It is to be understood that the drawings are for purposes ofillustrating the concepts of the disclosure and may not be to scale.

Anode Overview

FIG. 1 is a cross-sectional view according to some embodiments of thepresent disclosure. Anode 100 includes an electrically conductivecurrent collector 101 and a continuous porous lithium storage layer 107.In this embodiment, the electrically conductive current collector 101includes a metal oxide layer 105 provided over an electricallyconductive layer 103, for example an electrically conductive metallayer. The continuous porous lithium storage layer 107 is provided overmetal oxide layer 105. In some embodiments, the top of the continuousporous lithium storage layer 107 corresponds to a top surface 108 ofanode 100. In some embodiments the continuous porous lithium storagelayer 107 is in physical contact with the metal oxide layer. In someembodiments, the active material of the continuous porous lithiumstorage layer may extend partially into the metal oxide layer. In someembodiments the continuous porous lithium storage layer includes amaterial capable of forming an electrochemically reversible alloy withlithium. In some embodiments, the continuous porous lithium storagelayer includes silicon, germanium, tin or alloys thereof. In someembodiments the continuous porous lithium storage layer comprises atleast 40 atomic % silicon, germanium or a combination thereof. In someembodiments, the continuous porous lithium storage layer is provided bya chemical vapor deposition (CVD) process including, but not limited to,hot-wire CVD or a plasma-enhanced chemical vapor deposition (PECVD). Insome embodiments, the CVD storage layer deposition process may reduce aportion of the metal oxide layer to metal.

In the present disclosure, the continuous porous lithium storage layeris substantially free of nanostructures, e.g., in the form ofspaced-apart wires, pillars, tubes or the like, or in the form ofregular, linear vertical channels extending through the lithium storagelayer. FIG. 2 shows a cross-sectional view of a prior art anode 170 thatincludes some non-limiting examples of nanostructures, such as nanowires190, nanopillars 192, nanotubes 194 and nanochannels 196 provided over acurrent collector 180. The term “nanostructure” herein generally refersto an active material structure (for example, a structure of silicon,germanium or their alloys) having at least one cross-sectional dimensionthat is less than about 2,000 nm, other than a dimension approximatelynormal to an underlying substrate (such as a layer thickness) andexcluding dimensions caused by random pores and channels. Similarly, theterms “nanowires”, “nanopillars” and “nanotubes” refers to wires,pillars and tubes, respectively, at least a portion of which, have adiameter of less than 2,000 nm. “High aspect ratio” nanostructures havean aspect ratio greater than 4:1, where the aspect ratio is generallythe height or length of a feature (which may be measured along a featureaxis aligned at an angle of 45 to 90 degrees relative to the underlyingcurrent collector surface) divided by the width of the feature (whichmay be measured generally orthogonal to the feature axis). In someembodiments, the continuous porous lithium storage layer is considered“substantially free” of nanostructures when the anode has an average offewer than 10 nanostructures per 1600 square microns (in which thenumber of nanostructures is the sum of the number of nanowires,nanopillars, and nanotubes in the same unit area), such nanostructureshaving an aspect ratio of 4:1 or higher. Alternatively, there is anaverage of fewer than 1 such nanostructures per 1600 square micrometers.As noted below, the current collector may have a high surface roughnessor the surface layer may include nanostructures, but these features areseparate from the continuous porous lithium storage layer.

In some embodiments, deposition conditions are selected in combinationwith the metal oxide so that the continuous porous lithium storage layeris relatively smooth providing an anode with diffuse or totalreflectance of at least 10% at 550 nm, alternatively at least 20%(measured at the continuous porous lithium storage layer side). In someembodiments, the anode may have lower reflectance than cited above, forexample, by providing a current collector having a rough surface or bymodifying deposition conditions of the lithium storage layer.

The anode can be a continuous foil or sheet but can alternatively be amesh or have some other 3-dimensional structure. In some embodiments,the anode is flexible.

In some embodiments as shown in FIG. 3 , the current collector 301includes electrically conductive layer 303 and metal oxide layers (305a, 305 b) deposited on either side of the electrically conductive layer303 and continuous porous lithium storage layers (307 a, 307 b) aredisposed on both sides to form anode 300. Metal oxide layers 305 a and305 b may be the same or different with respect to composition,thickness, porosity or some other property. Similarly, continuous porouslithium storage layers 307 a and 307 b may be the same or different withrespect to composition, thickness, porosity or some other property.

In some embodiments, the current collector has a mesh structure and arepresentative cross section is shown in FIG. 4 . Current collector 401includes metal oxide layer 405 substantially surrounding the inner,electrically conductive core 403, e.g., a wire forming part of the mesh,the core acting as an electrically conductive layer. A continuous porouslithium storage layer 407 is provided over the metal oxide layer to formanode 400. The mesh can be formed from interwoven wires or ribbons ofmetal or conductive carbon, formed by patterning holes into a substrate,e.g., a metal or metal-coated sheet, or any suitable method known in theart.

Current Collector

Current collector (101, 301, 401) includes at least one metal oxidelayer (105, 305, 405), and may further include a separate electricallyconductive layer (103, 303, 403). The metal oxide may be stoichiometricor non-stoichiometric. The metal oxide layer may include a mixture ofmetal oxides having homogeneously or heterogeneously distributed oxidestoichiometries, mixtures of metals or both. If the metal oxide layer(105, 305, 405) has sufficient electrical conductivity to function as acurrent collector, the separate electrically conductive layer (103, 303,403) is optional. In embodiments using an electrically conductive layer,the metal oxide layer should be sufficiently electrically conductive(e.g., is at least semi-conducting, or non-insulating) to allow transferof electrical charge between the electrically conductive layer and thecontinuous porous lithium storage layer. The metal oxide layer mayinclude dopants or regions of unoxidized metal that promote electricalconductivity. In some embodiments the electrically conductive layer mayhave a conductivity of at least 10³ S/m, or alternatively at least 10⁶S/m, or alternatively at least 10⁷ S/m, and may include inorganic ororganic conductive materials or a combination thereof.

In some embodiments, the electrically conductive layer includes ametallic material, e.g., titanium (and its alloys), nickel (and itsalloys), copper (and its alloys), or stainless steel. In someembodiments, the electrically conductive layer includes an electricallyconductive carbon, such as carbon black, carbon nanotubes, graphene,graphene oxide, reduced graphene oxide, and graphite. In someembodiments the electrically conductive layer may be in the form of afoil or sheet of conductive material, or alternatively a layer depositedonto an insulating substrate (e.g., a polymer sheet coated withconductive material such as nickel or copper, optionally on both sides).

In some embodiments, the metal oxide layer includes a transition metaloxide, e.g., an oxide of nickel, titanium or copper. In someembodiments, the metal oxide layer includes an oxide of aluminum. Insome embodiments, the metal oxide layer is an electrically conductivedoped oxide, including but not limited to, indium-doped tin oxide (ITO)or an aluminum-doped zinc oxide (AZO). In some embodiments, the metaloxide layer includes an alkali metal oxide or alkaline earth metaloxide. In some embodiments the metal oxide layer includes an oxide oflithium. As mentioned, the metal oxide layer may include mixtures ofmetals. For example, an “oxide of nickel” may optionally include othermetals in addition to nickel. In some embodiments, the metal oxide layerincludes an oxide of an alkali metal or an alkaline earth metal (e.g.,lithium or sodium) along with an oxide of a transition metal (e.g.,nickel or copper). In some embodiments, the metal oxide layer mayinclude a small amount of hydroxide such that the ratio of oxygen atomsin the form of hydroxide relative to oxide is less than 0.25,respectively.

In some embodiments, the metal oxide layer has an average thickness ofat least 0.005 μm, alternatively at least 0.01 μm, alternatively atleast 0.02 μm, alternatively at least 0.05 μm, alternatively 0.1 μm,alternatively at least 0.2 μm, alternatively at least 0.5 μm. In someembodiments, the metal oxide layer has an average thickness in a rangeof about 0.005 μm to about 0.01 μm, alternatively about 0.01 μm to about0.02 μm, alternatively about 0.02 μm to about 0.05 μm, alternativelyabout 0.05 μm to about 0.1 μm, alternatively about 0.1 μm to about 0.2μm, alternatively about 0.2 μm to about 0.5 μm, alternatively about 0.5μm to about 1 μm, alternatively about 1 μm to about 2 μm, alternativelyabout 2 μm to about 5 μm, alternatively about 5 μm to about 1 μm, or anycombination of contiguous ranges thereof.

The metal oxide layer may include a stoichiometric oxide, anon-stoichiometric oxide or both. In some embodiments, the metal withinthe metal oxide layer may exist in multiple oxidation states. In someembodiments the metal oxide layer may have a gradient of oxygen contentwhere the atomic % of oxygen adjacent to an electrically conductivelayer is lower than the atomic % adjacent to the lithium storage layer.

In some embodiments, the metal oxide layer is formed directly by atomiclayer deposition (ALD), CVD, evaporation or sputtering. In someembodiments, the electrically conductive layer is a metal layer 103 andthe metal oxide layer is formed by oxidizing a portion of theelectrically conductive (metal) layer. For example, the metal can bethermally oxidized in the presence of oxygen, electrolytically oxidized,chemically oxidized in an oxidizing liquid or gaseous medium or the liketo form the metal oxide layer.

In some embodiments, a metal oxide layer precursor composition may becoated or printed over the electrically conductive layer 103 thentreated to form metal oxide layer 105. Some non-limiting examples ofmetal oxide precursor compositions include sol-gels (metal alkoxides),metal carbonates, metal acetates (including organic acetates), metalhydroxides and metal oxide dispersions. The metal oxide precursorcomposition may be thermally treated to form the metal oxide layer. Insome embodiments, room temperature may be sufficient temperature tothermally treat the precursor. In some embodiments, a metal oxideprecursor composition is thermally treated by exposure to a temperatureof at least 50° C., alternatively in a range of 50° C. to 150° C.,alternatively in a range of 150° C. to 250° C., alternatively in a rangeof 250° C. to 350° C., alternatively in a range of 350° C. to 450° C.,or any combination of these ranges. Thermal treatment time to form themetal oxide layer from the precursor depends on many factors, but may bein a range of about 0.1 min to about 1 min, alternatively about 1 min toabout 5 mins, alternatively about 5 mins to about 10 mins, alternativelyabout 10 mins to about 30 minutes, alternatively about 30 mins to about60 mins, alternatively about 60 mins to about 90 mins, alternatively ina range of about 90 mins to about 120 mins, or any combination ofcontiguous ranges thereof. In some embodiments, thermal treatment may becarried out using an oven, infrared heating elements, contact with aheated surface (e.g., a hot plate) or exposure to a flash lamp. In someembodiments, the metal oxide precursor composition is treated byexposure to reduced pressure to form the metal oxide, e.g., to drive offsolvents or volatile reaction products. The reduced pressure may be lessthan 100 Torr, alternatively in a range of 0.1 to 100 Torr. Exposuretime to the reduced pressure may be in a range of about 0.1 min to about1 min, alternatively about 1 min to about 5 mins, alternatively about 5mins to about 10 mins, alternatively about 10 mins to about 30 minutes,alternatively about 30 mins to about 60 mins, alternatively about 60mins to about 90 mins, alternatively in a range of about 90 mins toabout 120 mins, or any combination of contiguous ranges thereof. In someembodiments, both reduced pressure and thermal treatment may be used.

In some embodiments, the metal oxide layer precursor compositionincludes a metal, e.g., metal-containing particles, that is treated withan oxidant (e.g., as previously described) under conditions where theoxide layer precursor is readily oxidized but underlying electricallyconductive layer is less so. The metal oxide precursor composition mayinclude a metal that is the same as or different from the metal(s) ofthe electrically conductive layer. In some embodiments, multiple metalprecursor compositions may be used to form a pattern of different metaloxides or multilayer structure of different metal oxides.

In some embodiments, the electrically conductive layer includes a meshor sheet of electrically conductive carbon, including but not limitedto, those formed from bundled carbon nanotubes or nanofibers. In someembodiments, such carbon-based electrically conductive layers mayinclude a surface layer of a conductive metal, e.g., nickel, copper,zinc, titanium or the like. In some embodiments, the conductive metalsurface layer may be applied by electrolytic or electroless platingmethods. The metal surface layer may be partially or full oxidized toform the corresponding metal oxide layer. In some embodiments, a porousmetal oxide may have a density lower than the density of a non-porousmetal oxide. In some embodiments, the density of a porous metal oxide isin a range of 50% to 60% of the density of a non-porous metal oxide,alternatively 60% to 70%, alternatively 70% to 80%, alternatively 80% to90%, alternatively 90% to 95%, alternatively 95% to 99%, or anycombination of contiguous ranges thereof.

In some embodiments, the metal oxide is formed in the same chamber as,or in line with, a tool used to deposit the continuous porous lithiumstorage layer. Doped metal oxide layers can be formed by adding dopantsor dopant precursors during the metal oxide formation step, oralternatively by adding dopants or dopant precursors to a surface of anelectrically conductive layer prior to the metal oxide layer formationstep, or alternatively treating a metal oxide layer with a dopant ordopant precursor after initial formation of the metal oxide layer. Insome embodiments, the metal oxide layer itself may have some reversibleor irreversible lithium storage capacity. In some embodiments, thereversible capacity of the metal oxide layer is lower than that of thecontinuous porous lithium storage layer. In some embodiments, the metaloxide layer may be porous.

In some embodiments, the metal oxide may be provided in a pattern overthe electrically conductive layer as disclosed in U.S. patentapplication Ser. No. 16/909,008, the entire contents of which areincorporated herein for all purposes.

In some embodiments, the metal oxide is formed by oxidizing a surfaceregion of a metal substrate, for example, oxidation of a metal foil suchas nickel foil. The non-oxidized portion of the metal foil acts as theelectrically conductive layer and the oxidized portion corresponds tothe metal oxide layer. This method is amenable to high-volume andlow-cost production of current collectors. The oxidation conditionsdepend upon the metal/metal surface, the target oxide thickness and thedesired oxide porosity. Unless otherwise stated, any reference to aparticular metal includes alloys of that metal. For example, nickel foilmay include pure nickel or any alloy of nickel wherein nickel is theprimary component. In some embodiments, an alloy metal also oxidizes,and the oxide of nickel formed from the alloy may include thatcorresponding oxidized metal. In some embodiments, the current collectoris formed by oxidation of a nickel substrate, e.g., a nickel foil, in afurnace under air brought to a temperature of at least 300° C.,alternatively at least 400° C., for example in a range of about 600° C.to about 900° C., or alternatively higher temperatures. The hold timedepends upon the selected temperature and the desired thickness/porosityfor the metal oxide layer. Typically, the oxidation hold time will be ina range of about 1 minute to about 2 hours, but shorter or longer timesare contemplated. A surface pretreatment step may be applied to promoteor otherwise control oxidation. Other metals such as copper and titaniummay have other operational hold times, temperatures and pretreatmentsaccording to their propensity to be oxidized.

The current collector may have an electrically conductive layer thatincludes two or more sublayers differing in chemical composition. Forexample, the current collector may include metallic copper foil as afirst electrically conductive sublayer, a second electrically conductivesublayer of metallic nickel provided over the copper, and a layer of anickel oxide over the metallic nickel. As mentioned previously, themetallic copper and nickel may be in the form of alloys. Similarly, themetal oxide layer may include two or more sublayers differing inchemical composition. For example, the current collector may include ametallic copper foil, a layer of a copper oxide over the copper foil anda layer of titanium dioxide over the copper oxide. FIG. 5 is a crosssectional view that illustrates these embodiments. Anode 500 of FIG. 5includes electrically conductive current collector 501 having metaloxide layer 505 provided over electrically conductive layer 503.Electrically conductive layer 503 is divided into first and secondelectrically conductive sublayers 503 a and 503 b, respectively, andmetal oxide layer 505 is divided into first and second metal oxidesublayers 505 a and 505 b, respectively. Continuous porous lithiumstorage layer 507 is formed over second metal oxide sublayer 505 b. Suchsublayers may be discrete or take the form of a gradient in chemicalcomposition. In some embodiments there may be a gradient or transitionzone between the electrically conductive layer(s) and the metal oxidelayer(s).

In some embodiments (not shown), an electrically conductive currentcollector may initially have an electrically conductive layer havingmetal sublayers such that a second metal sublayer at the surface is moreeasily oxidized than an underlying first metal sublayer. Under oxidationconditions to form the current collector, only the second sublayeroxidizes (all or just a portion). This may allow for better control ofthe thickness of the metal oxide layer.

Continuous Porous Lithium Storage Layer

The continuous porous lithium storage layer includes a porous materialcapable of reversibly incorporating lithium. In some embodiments, thecontinuous porous lithium storage layer includes silicon, germanium or amixture of both. In some embodiments, the continuous porous lithiumstorage layer includes antimony or tin. In some embodiments, thecontinuous porous lithium storage layer is substantially amorphous. Insome embodiments, the continuous porous lithium storage layer includessubstantially amorphous silicon. Such substantially amorphous storagelayers may include a small amount (e.g., less than 20 atomic %) ofcrystalline material dispersed therein. The continuous porous lithiumstorage layer may include dopants such as hydrogen, boron, phosphorous,sulfur, fluorine, aluminum, gallium, indium, arsenic, antimony, bismuth,nitrogen, or metallic elements. In some embodiments the continuousporous lithium storage layer may include porous substantially amorphoushydrogenated silicon (a-Si:H), having, e.g., a hydrogen content of from0.1 to 20 atomic %, or alternatively higher. In some embodiments, thecontinuous porous lithium storage layer may include methylated amorphoussilicon. Note that, unless referring specifically to hydrogen content,any atomic % metric used herein for a lithium storage material or layerrefers to all atoms other than hydrogen.

In some embodiments, the continuous porous lithium storage layerincludes at least 40 atomic % silicon, germanium or a combinationthereof, alternatively at least 50 atomic %, alternatively at least 60atomic %, alternatively at least 70 atomic %, alternatively, at least 80atomic %, alternatively at least 90 atomic %. In some embodiments, thecontinuous porous lithium storage layer includes at least 40 atomic %silicon, alternatively at least 50 atomic %, alternatively at least 60atomic %, alternatively at least 70 atomic %, alternatively, at least 80atomic %, alternatively at least 90 atomic %, alternatively at least 95atomic %, alternatively at least 97 atomic %.

In some embodiments, the continuous porous lithium storage layerincludes less than 10 atomic % carbon, alternatively less than 5 atomic%, alternatively less than 2 atomic %, alternatively less than 1 atomic%, alternatively less than 0.5 atomic %. In some embodiments, thecontinuous porous lithium storage layer includes less than 5% by weight,alternatively less than 1% by weight, of carbon-based binders, carbonnanotubes, graphitic carbon, graphene, graphene oxide, reduced grapheneoxide, carbon black, and conductive carbon.

The continuous porous lithium storage layer includes voids orinterstices (pores), which may be random or non-uniform with respect tosize, shape and distribution. Such porosity does not result in, or aresult from, the formation of any recognizable nanostructures such asnanowires, nanopillars, nanotubes, nanochannels or the like. In someembodiments, the pores are polydisperse. In some embodiments, whenanalyzed by SEM cross section, 90% of pores larger than 100 nm in anydimension are smaller than about 5 μm in any dimension, alternativelysmaller than about 3 μm, alternatively smaller than about 2 μm. In someembodiments, the continuous porous lithium storage layer may includesome pores that are smaller than 100 nm in any dimension, alternativelysmaller than 50 nm in any dimension, alternatively smaller than 20 nm inany dimension. In some embodiments the continuous porous lithium storagelayer has an average density in a range of 1.0-1.1 g/cm3, alternatively1.1-1.2 g/cm3, alternatively 1.2-1.3 g/cm3, alternatively 1.3-1.4 g/cm3,alternatively 1.4-1.5 g/cm3, alternatively 1.5-1.6 g/cm3, alternatively1.6-1.7 g/cm3, alternatively 1.7-1.8 g/cm3, alternatively 1.8-1.9 g/cm3,alternatively 1.9-2.0 g/cm3, alternatively 2.0-2.1 g/cm3, alternatively2.1-2.2 g/cm3, alternatively 2.2-2.25 g/cm3, or any combination ofcontiguous ranges thereof, and includes at least 40 atomic % silicon,alternatively at least 50 atomic % silicon, alternatively at least 60atomic % silicon, alternatively at least 70 atomic % silicon,alternatively 80 atomic % silicon, alternatively at least 90 atomic %silicon, alternatively at least 95 atomic % silicon.

In some embodiments, the majority of active material (e.g., silicon,germanium or alloys thereof) of the continuous porous lithium storagelayer has substantial lateral connectivity across portions of thecurrent collector creating, such connectivity extending around randompores and interstices (as discussed later). Referring again to FIG. 1 ,in some embodiments, “substantial lateral connectivity” means thatactive material at one point X in the continuous porous lithium storagelayer 107 may be connected to active material at a second point X′ inthe layer at a straight-line lateral distance LD that is at least asgreat as the thickness T of the continuous porous lithium storage layer,alternatively, a lateral distance at least 2 times as great as thethickness, alternatively, a lateral distance at least 3 times as greatas the thickness. Not shown, the total path distance of materialconnectivity, including circumventing pores, may be longer than LD. Insome embodiments, the continuous porous lithium storage layer may bedescribed as a matrix of interconnected silicon, germanium or alloysthereof, with random pores and interstices embedded therein. In someembodiments, the continuous porous lithium storage layer has asponge-like form. In some embodiments, about 75% or more of the metaloxide layer surface is contiguous with the continuous porous lithiumstorage layer, at least prior to electrochemical formation. It should benoted that the continuous porous lithium storage layer does notnecessarily extend across the entire anode without any lateral breaksand may include random discontinuities or cracks and still be consideredcontinuous.

In some embodiments, the continuous porous lithium storage layerincludes a substoichiometric oxide of silicon (SiO_(x)), germanium(GeO_(x)) or tin (SnO_(x)) wherein the ratio of oxygen atoms to silicon,germanium or tin atoms is less than 2:1, i.e., x<2, alternatively lessthan 1:1, i.e., x<1. In some embodiments, x is in a range of 0.02 to0.95, alternatively 0.02 to 0.10, alternatively 0.10 to 0.50, oralternatively 0.50 to 0.95, alternatively 0.95 to 1.25, alternatively1.25 to 1.50, or any combination of contiguous ranges thereof.

In some embodiments, the continuous porous lithium storage layerincludes a substoichiometric nitride of silicon (Si_(x)N_(y)), germanium(GeN_(y)) or tin (SnN_(y)) wherein the ratio of nitrogen atoms tosilicon, germanium or tin atoms is less than 1.25:1, i.e., y<1.25. Insome embodiments, y is in a range of 0.02 to 0.95, alternatively 0.02 to0.10, alternatively 0.10 to 0.50, or alternatively 0.50 to 0.95,alternatively 0.95 to 1.20, or any combination of contiguous rangesthereof.

In some embodiments, the continuous porous lithium storage layerincludes a substoichiometric oxynitride of silicon (SiO_(x)N_(y)),germanium (GeO_(x)N_(y)), or tin (SnO_(x)N_(y)) wherein the ratio oftotal oxygen and nitrogen atoms to silicon, germanium or tin atoms isless than 1:1, i.e., (x+y)<1. In some embodiments, (x+y) is in a rangeof 0.02 to 0.95, alternatively 0.02 to 0.10, alternatively 0.10 to 0.50,or alternatively 0.50 to 0.95, or any combination of contiguous rangesthereof.

In some embodiments, the above sub-stoichiometric oxides, nitrides oroxynitrides are provided by a CVD process, including but not limited to,a PECVD process. The oxygen and nitrogen may be provided uniformlywithin the continuous porous lithium storage layer, or alternatively theoxygen or nitrogen content may be varied as a function of storage layerthickness.

Referring to FIG. 6 , anode 600 includes continuous porous lithiumstorage layer 607 provided over current collector 601 including metaloxide layer 605 and electrically conductive layer 603. In someembodiments, continuous porous lithium storage layer 607 includes aplurality of continuous porous lithium storage sublayers (607 a and 607b) having different physical properties or chemical compositions, andindependently selected from any of the embodiments discussed above. Forexample, lithium storage sublayer 607 a may include amorphous siliconwith low oxygen content and lithium storage sublayer 607 b may include asuboxide of silicon, SiO_(x), with x in a range of 0.02 to 0.95.Alternatively, the compositions of 607 a and 607 b could be reversed. Inanother example, lithium storage sublayer 607 a may include amorphoussilicon with low germanium and lithium storage sublayer 607 b includes ahigher atomic % germanium than 607 a. In some embodiments, the lithiumstorage sublayers may have different amounts or types of dopants. Insome other embodiments, lithium storage sublayers 607 a and 607 b havesimilar chemical compositions, but the density of 607 a is higher than607 b. These are just a few non-limiting examples. Many othercombinations are possible. Although two lithium storage sublayers areshown in FIG. 6 , three or more sublayers may instead be used.

In some embodiments, the continuous porous lithium storage layerincludes a gradient of components, density, or porosity, or acombination thereof, as a function of layer thickness. For example, thecontinuous porous lithium storage layer 107 may include amorphoussilicon having a density higher near the metal oxide layer 105 than nearthe top surface 108, or vice versa.

Additional Lithium Storage Layers

The generally planar nature of some embodiments of the present anodefurther allows simple coating of additional lithium storage layers thatare not continuous porous lithium storage layers as described herein.For example, conventional lithium-ion battery slurries based on carbonthat may optionally further include silicon particles, may be coatedover the continuous porous lithium storage layer of the presentdisclosure to further enhance charge capacity. Coating methods mayinclude curtain coating, slot coating, spin coating, ink jet coating,spray coating or any other suitable method.

CVD

CVD generally involves flowing a precursor gas, a gasified liquid interms of direct liquid injection CVD or gases and liquids into a chambercontaining one or more objects, typically heated, to be coated. Chemicalreactions occur on and near the hot surfaces, resulting in thedeposition of a thin film on the surface. This is accompanied by theproduction of chemical by-products that are exhausted out of the chamberalong with unreacted precursor gases. As would be expected with thelarge variety of materials deposited and the wide range of applications,there are many variants of CVD that may be used to form the lithiumstorage layer, the metal oxide layer, a supplemental layer (see below)or other layer. It may be done in hot-wall reactors or cold-wallreactors, at sub-torr total pressures to above-atmospheric pressures,with and without carrier gases, and at temperatures typically rangingfrom 100-1600° C. in some embodiments. There are also a variety ofenhanced CVD processes, which involve the use of plasmas, ions, photons,lasers, hot filaments, or combustion reactions to increase depositionrates and/or lower deposition temperatures. Various process conditionsmay be used to control the deposition, including but not limited to,temperature, precursor material, gas flow rate, pressure, substratevoltage bias (if applicable), and plasma energy (if applicable).

As mentioned, the continuous porous lithium storage layer, e.g., a layerof silicon or germanium or both, may be provided by plasma-enhancedchemical vapor deposition (PECVD). Relative to conventional CVD,deposition by PECVD can often be done at lower temperatures and higherrates, which can be advantageous for higher manufacturing throughput. Insome embodiments, the PECVD is used to deposit a substantially amorphoussilicon layer (optionally doped) over the metal oxide layer. In someembodiments, PECVD is used to deposit a substantially amorphouscontinuous porous silicon layer over the metal oxide layer.

PECVD

In PECVD processes, according to various implementations, a plasma maybe generated in a chamber in which the substrate is disposed or upstreamof the chamber and fed into the chamber. Various types of plasmas may beused including, but not limited to, capacitively-coupled plasmas,inductively-coupled plasmas, and conductive coupled plasmas. Anyappropriate plasma source may be used, including DC, AC, RF, VHF,combinatorial PECVD and microwave sources may be used. Some non-limitingexamples of useful PECVD tools include hollow cathode tube PECVD,magnetron confined PECVD, inductively coupled plasma chemical vapordeposition (ICP-PECVD, sometimes called HDPECVD, ICP-CVD or HDCVD), andexpanding thermal plasma chemical vapor deposition (ETP-PECVD).

PECVD process conditions (temperatures, pressures, precursor gases,carrier gasses, dopant gases, flow rates, energies, and the like) canvary according to the particular process and tool used, as is well knownin the art

In some implementations, the PECVD process is an expanding thermalplasma chemical vapor deposition (ETP-PECVD) process. In such a process,a plasma generating gas is passed through a direct current arc plasmagenerator to form a plasma, with a web or other substrate including thecurrent collector optionally in an adjoining vacuum chamber. A siliconsource gas is injected into the plasma, with radicals generated. Theplasma is expanded via a diverging nozzle and injected into the vacuumchamber and toward the substrate. An example of a plasma generating gasis argon (Ar). In some embodiments, the ionized argon species in theplasma collide with silicon source molecules to form radical species ofthe silicon source, resulting in deposition onto the current collector.Example ranges for voltages and currents for the DC plasma source are 60to 80 volts and 40 to 70 amperes, respectively.

Any appropriate silicon source may be used to deposit silicon, includingsilane (SiH₄), dichlorosilane (H₂SiCl₂), monochlorosilane (H₃SiCl),trichlorosilane (HSiCl₃), silicon tetrachloride (SiCl₄), anddiethylsilane. Depending on the gas(es) used, the silicon layer may beformed by decomposition or reaction with another compound, such as byhydrogen reduction. In some embodiments, the gases may include a siliconsource such as silane, a noble gas such as helium, argon, neon, orxenon, optionally one or more dopant gases, and substantially nohydrogen. In some embodiments, the gases may include argon, silane, andhydrogen, and optionally some dopant gases. In some embodiments the gasflow ratio of argon relative to the combined gas flows for silane andhydrogen is at least 3.0, alternatively at least 4.0. In someembodiments, the gas flow ratio of argon relative to the combined gasflows for silane and hydrogen is in a range of 3-5, alternatively 5-10,alternatively 10-15, alternatively 15-20, or any combination ofcontiguous ranges thereof. In some embodiments, the gas flow ratio ofhydrogen gas to silane gas is in a range of 0-0.1, alternatively0.1-0.2, alternatively 0.2-0.5, alternatively 0.5-1, alternatively 1-2,alternatively 2-5, or any combination of contiguous ranges thereof. Insome embodiments, higher porosity silicon may be formed and/or the rateof silicon deposition may be increased when the gas flow ratio of silanerelative to the combined gas flows of silane and hydrogen increases. Insome embodiments a dopant gas is borane or phosphine, which may beoptionally mixed with a carrier gas. In some embodiments, the gas flowratio of dopant gas (e.g., borane or phosphine) to silicon source gas(e.g., silane) is in a range of 0.0001-0.0002, alternatively0.0002-0.0005, alternatively 0.0005-0.001, alternatively 0.001-0.002,alternatively 0.002-0.005, alternatively 0.005-0.01, alternatively0.01-0.02, alternatively 0.02-0.05, alternatively 0.05-0.10, or anycombination of contiguous ranges thereof. Such gas flow ratios describedabove may refer to the relative gas flow, e.g., in standard cubiccentimeter per minute (SCCM). In some embodiments, the PECVD depositionconditions and gases may be changed over the course of the deposition.

In some embodiments, the temperature at the current collector during atleast a portion of the time of PECVD deposition is in a range of 100° C.to 200° C., alternatively 200° C. to 300° C., alternatively 300° C. to400° C., alternatively 400° C. to 500° C., alternatively 500° C. to 600°C., or any combination of contiguous ranges thereof. In someembodiments, the temperature may vary during the time of PECVDdeposition. For example, the temperature during early times of the PECVDmay be higher than at later times. Alternatively, the temperature duringlater times of the PECVD may be higher than at earlier times.

The thickness or mass per unit area of the continuous porous lithiumstorage layer depends on the storage material, desired charge capacityand other operational and lifetime considerations. Increasing thethickness typically provides more capacity. If the continuous porouslithium storage layer becomes too thick, electrical resistance mayincrease and the stability may decrease. In some embodiments, the anodemay be characterized as having an active silicon areal density of atleast 0.5 mg/cm2, alternatively at least 1.0 mg/cm2, alternatively atleast 1.5 mg/cm2, alternatively at least 3 mg/cm2, alternatively atleast 5 mg/cm2. In some embodiments, the lithium storage structure maybe characterized as having an active silicon areal density in a range of0.5-1.5 mg/cm2, alternatively 1.5-2 mg/cm2, alternatively in a range of2-3 mg/cm2, alternatively in a range of 3-5 mg/cm2, alternatively in arange of 5-10 mg/cm2, alternatively in a range of 10-15 mg/cm2,alternatively in a range of 15-20 mg/cm2, or any combination ofcontiguous ranges thereof. “Active areal silicon density” refers to thesilicon in electrical communication with the current collector that isavailable for reversible lithium storage at the beginning of cellcycling, e.g., after anode “electrochemical formation” discussed later.“Areal” of this term refers to the surface area of the electricallyconductive layer over which active silicon is provided. In someembodiments, not all of the silicon content is active silicon, i.e.,some may be tied up in the form of non-active silicides or electricallyisolated from the current collector.

In some embodiments the continuous porous lithium storage has an averagethickness of at least 0.5 μm, alternatively at least 1 μm, alternativelyat least 3 μm, alternatively at least 7 μm. In some embodiments, thecontinuous porous lithium storage layer has an average thickness in arange of about 0.5 μm to about 50 μm. In some embodiments, thecontinuous porous lithium storage layer comprises at least 85 atomic %amorphous silicon and has a thickness in a range of 0.5 to 1 μm,alternatively 1-2 μm, alternatively 2-4 μm, alternatively 4-7 μm,alternatively 7-10 μm, alternatively 10-15 μm, alternatively 15-20 μm,alternatively 20-25 μm, alternatively 25-30 μm, alternatively 30-40 μm,alternatively 40-50 μm, or any combination of contiguous ranges thereof.

In some embodiments, the continuous porous lithium storage layerincludes silicon but does not contain a substantial amount ofcrystalline silicides, i.e., the presence of silicides is not readilydetected by X-Ray Diffraction (XRD). Metal silicides, e.g., nickelsilicide, commonly form when silicon is deposited at higher temperaturesdirectly onto metal, e.g., nickel foil. Metal silicides such as nickelsilicides often have much lower lithium storage capacity than siliconitself. In some embodiments, the average atomic % of silicide-formingmetallic elements within the continuous porous lithium storage layer areon average less than 35%, alternatively less than 20%, alternativelyless than 10%, alternatively less than 5%. In some embodiments, theaverage atomic % of silicide-forming metallic elements within thecontinuous porous lithium storage layer are in a range of about 0.01% toabout 10%, alternatively about 0.05 to about 5%. In some embodiments,the atomic % of silicide forming metallic elements in the continuousporous lithium storage layer is higher nearer the current collector thanaway from the current collector.

Other Anode Features

In some embodiments, the anode may further include one or moresupplemental layers. As shown in FIG. 7A, a supplemental layer 750 isprovided over the surface of the continuous porous lithium storage layer707, which overlays current collector 701 including metal oxide layer705 and electrically conductive layer 703. In some embodiments, thesupplemental layer is a protection layer to enhance lifetime or physicaldurability. The supplemental layer may be an oxide or nitride formedfrom the lithium storage material itself, e.g., silicon dioxide, siliconnitride, or silicon oxynitride in the case of silicon. A supplementallayer may be deposited, for example, by ALD, CVD, PECVD, evaporation,sputtering, solution coating, ink jet or any method that is compatiblewith the anode. In some embodiments, a supplemental layer is depositedin the same CVD or PECVD device as the continuous lithium storage layer.For example, stoichiometric silicon dioxide or silicon nitridesupplemental layer by be formed by introducing an oxygen- ornitrogen-containing gas (or both) along with the silicon precursor gasused to form the continuous porous lithium storage layer. In someembodiments the supplemental layer may include boron nitride or siliconcarbide. In some embodiments, supplemental layer 750 may include a metalcompound as described below.

As shown in FIG. 7B, in some embodiments, the anode includes a firstsupplemental layer 750-1 and a second supplemental layer 750-2overlaying the first supplemental layer and having a chemicalcomposition different than the first supplemental layer. In someembodiments, the first supplemental layer 750-1 may include siliconnitride, silicon dioxide, silicon oxynitride, or a first metal compound.The second supplemental layer 750-2 has a composition different from thefirst supplemental layer and may include silicon nitride, silicondioxide, silicon oxynitride, or a second metal compound. In someembodiments, the second supplemental layer may be in contact with thefirst supplemental layer. In some embodiments, one or more additionalsupplemental layers may be provided over the second supplemental layer.In some embodiments having two or more supplemental layers, eachsupplemental layer is in contact with at least one other supplementallayer.

In some embodiments, the first supplemental layer 750-1 and the optionalsecond or additional supplemental layers may help stabilize thecontinuous porous lithium storage layer by providing a barrier to directelectrochemical reactions with solvents or electrolytes that can degradethe interface. A supplemental layer should be reasonably conductive tolithium ions and permit lithium ions to move into and out of thecontinuous porous lithium storage layer during charging and discharging.In some embodiments, the lithium ion conductivity of a supplementallayer is at least 10⁻⁹ S/cm, alternatively at least 10⁻⁸ S/cm,alternatively at least 10⁻⁷ S/cm, alternatively at least 10⁻⁶ S/cm. Insome embodiments, the supplemental layer acts as a solid-stateelectrolyte. In some embodiments, the supplemental layer(s) are lesselectrically conductive than the lithium storage structure so thatlittle or no electrochemical reduction of lithium ions to lithium metaloccurs at the supplemental layer/electrolyte interface. In addition toproviding protection from electrochemical reactions, the multiplesupplemental layer structure embodiments may provide superior structuralsupport. In some embodiments, although the supplemental layers may flexand may form fissures when the continuous porous lithium storage layerexpands during lithiation, crack propagation can be distributed betweenthe layers to reduce direct exposure of the lithium storage structure tothe bulk electrolyte. For example, a fissure in the second supplementallayer may not align with a fissure in the first supplemental layer. Suchan advantage may not occur if just one thick supplemental layer is used.In an embodiment, the second supplemental layer may be formed of amaterial having higher flexibility than the first supplemental layer.

In some embodiments, a supplemental layer (the first supplemental layer,the second supplemental layer, or any additional supplemental layer(s))may include silicon nitride, e.g., substantially stoichiometric siliconnitride where the ratio of nitrogen to silicon is in a range of 1.33 to1.25. A supplemental layer comprising silicon nitride may have anaverage thickness in a range of about 0.5 nm to 1 nm, alternatively 1 nmto 2 nm, alternatively 2 nm to 10 nm, alternatively 10 nm to 20 nm,alternatively 20 nm to 30 nm, alternatively 30 nm to 40 nm,alternatively 40 nm to 50 nm, or any combination of contiguous rangesthereof. Silicon nitride may be deposited by an atomic layer deposition(ALD) process or by a CVD process. In some embodiments, the continuousporous lithium storage layer includes silicon deposited by some type ofCVD process as described above, and at the end, a nitrogen gas source isadded to the CVD deposition chamber along with the silicon source.

In some embodiments, a supplemental layer (the first supplemental layer,the second supplemental layer, or any additional supplemental layer(s))may include silicon dioxide, e.g., substantially stoichiometric silicondioxide where the ratio of oxygen to silicon is in a range of 2.0 to1.9. A supplemental layer comprising silicon dioxide may have an averagethickness in a range of about 2 nm to 10 nm, alternatively 10 nm to 30nm, alternatively 30 nm to 50 nm, alternatively 50 nm to 70 nm,alternatively 70 nm to 100 nm, alternatively 100 nm to 150 nm,alternatively 150 nm to 200 nm, or any combination of contiguous rangesthereof. Silicon dioxide may be deposited by an atomic layer deposition(ALD) process or by a CVD process. In some embodiments, the continuousporous lithium storage layer includes silicon deposited by some type ofCVD process as described above, and at the end, an oxygen-containing gassource is added to the CVD deposition chamber along with the siliconsource.

In some embodiments, a supplemental layer (the first supplemental layer,the second supplemental layer, or any additional supplemental layer(s))may include silicon oxynitride, e.g., a substantially stoichiometricoxynitride of silicon (SiO_(x)N_(y)) wherein the sum of 0.5x and 0.75yis in a range of 1.00 to 0.95. A supplemental layer comprising siliconnitride may have an average thickness in a range of about 0.5 nm to 1nm, alternatively 1 nm to 2 nm, alternatively 2 nm to 10 nm,alternatively 10 nm to 20 nm, alternatively 20 nm to 30 nm,alternatively 30 nm to 40 nm, alternatively 40 nm to 50 nm,alternatively 50 nm to 70 nm, alternatively 70 nm to 100 nm,alternatively 100 nm to 150 nm, or any combination of contiguous rangesthereof. In some embodiments, silicon oxynitride may be provided by aCVD process, including but not limited to, a PECVD process. The oxygenand nitrogen may be provided uniformly within the continuous porouslithium storage layer, or alternatively the oxygen or nitrogen contentmay be varied as a function of position (e.g., height) within thestorage layer.

In some embodiments, silicon nitride, silicon dioxide, or siliconoxynitride may be deposited by an atomic layer deposition (ALD) processor by a CVD process. In some embodiments, the continuous porous lithiumstorage layer includes silicon deposited by some type of CVD process asdescribed above, and at the end, a nitrogen- and/or an oxygen-containinggas source is added to the CVD deposition chamber along with the siliconsource.

In some embodiments a supplemental layer (the first supplemental layer,the second supplemental layer, or any additional supplemental layer(s))may include a metal oxide, metal nitride, or metal oxynitride, e.g.,those containing aluminum, titanium, vanadium, zirconium, or tin, ormixtures thereof. In some embodiments, a supplemental layer including ametal oxide, metal nitride, or metal oxynitride, may have an averagethickness of less than about 100 nm, for example, in a range of about0.5 nm to about 1 nm, alternatively about 1 nm to about 2 nm,alternatively 2 nm to 10 nm, alternatively 10 nm to 20 nm, alternatively20 nm to 30 nm, alternatively 30 nm to 40 nm, alternatively 40 nm to 50nm, or any combination of contiguous ranges thereof. The metal oxide,metal nitride, or metal oxynitride may include other components ordopants such as transition metals, phosphorous or silicon.

In some embodiments, the metal compound may include a lithium-containingmaterial such as lithium phosphorous oxynitride (LIPON), a lithiumphosphate, a lithium aluminum oxide, or a lithium lanthanum titanate. Insome embodiments, the thickness of supplemental layer including alithium-containing material may be in a range of 0.5 nm to 200 nm,alternatively 1 nm to 10 nm, alternatively 10 nm to 20 nm, alternatively20 nm to 30 nm, alternatively 30 nm to 40 nm, alternatively 40 nm to 50nm, alternatively 50 nm to 100 nm, alternatively 100 to 200 nm, or anycombination of contiguous ranges thereof.

In some embodiments the metal compound may be deposited by a processcomprising ALD, thermal evaporation, sputtering, or e-beam evaporation.ALD is a thin-film deposition technique typically based on thesequential use of a gas phase chemical process. The majority of ALDreactions use at least two chemicals, typically referred to asprecursors. These precursors react with the surface of a material one ata time in a sequential, self-limiting, manner. Through the repeatedexposure to separate precursors, a thin film is deposited, often in aconformal manner. In addition to conventional ALD systems, so-calledspatial ALD (SALD) methods and materials can be used, e.g., as describedU.S. Pat. No. 7,413,982, the entire contents of which are incorporatedby reference herein for all purposes. In certain embodiments, SALD canbe performed under ambient conditions and pressures and have higherthroughput than conventional ALD systems.

In some embodiments, the process for depositing the metal compound mayinclude electroless deposition, contact with a solution, contact with areactive gas, or electrochemical methods. In some embodiments, a metalcompound may be formed by depositing a metallic layer (including but notlimited to thermal evaporation, CVD, sputtering, e-beam evaporation,electrochemical deposition, or electroless deposition) followed bytreatment to convert the metal to the metal compound (including but notlimited to, contact with a reactive solution, contact with an oxidizingagent, contact with a reactive gas, or a thermal treatment).

The supplemental layer may include an inorganic-organic hybrid structurehaving alternating layers of metal oxide and bridging organic materials.These inorganic-organic hybrid structures are sometimes referred to as“metalcone”. Such structures can be made using a combination of atomiclayer deposition to apply the metal compound and molecular layerdeposition (MLD) to apply the organic. The organic bridge is typically amolecule having multiple functional groups. One group can react with alayer comprising a metal compound and the other group is available toreact in a subsequent ALD step to bind a new metal. There is a widerange of reactive organic functional groups that can be used including,but not limited to hydroxy, carboxylic acid, amines, acid chlorides andanhydrides. Almost any metal compound suitable for ALD deposition can beused. Some non-limiting examples include ALD compounds for aluminum(e.g., trimethyl aluminum), titanium (e.g., titanium tetrachloride),zinc (e.g., diethyl zinc), and zirconium(tris(dimethylamino)cyclopentadienyl zirconium). For the purposes of thepresent disclosure, this alternating sublayer structure of metaloxide/bridging organic is considered a single supplemental layer ofmetalcone. When the metal compound includes aluminum, such structuresmay be referred to as an alucone. Similarly, when the metal compoundincludes zirconium, such structures may be referred to as a zircone.Further examples of inorganic-organic hybrid structures that may besuitable as a supplemental layer may be found in U.S. Pat. No.9,376,455, and US patent publications 2019/0044151 and 2015/0072119, theentire contents of which are incorporated herein by reference.

In some embodiments, a supplemental layer having a metalcone may have athickness in a range of 0.5 nm to 200 nm, alternatively 1 nm to 10 nm,alternatively 10 nm to 20 nm, alternatively 20 nm to 30 nm,alternatively 30 nm to 40 nm, alternatively 40 nm to 50 nm,alternatively 50 nm to 100 nm, alternatively 100 to 200 nm, or anycombination of contiguous ranges thereof.

In some embodiments a supplemental layer (a first, a second, or anadditional supplemental layer) may include boron nitride or siliconcarbide and may have an average thickness of less than about 100 nm, forexample, in a range of about 0.5 nm to about 1 nm, alternatively about 1nm to about 2 nm, alternatively 2 nm to 10 nm, alternatively 10 nm to 20nm, alternatively 20 nm to 30 nm, alternatively 30 nm to 40 nm,alternatively 40 nm to 50 nm, or any combination of contiguous rangesthereof.

In some embodiments the anode is at least partially pre-lithiated, i.e.,the continuous porous lithium storage layer and/or the metal oxide layerincludes some lithium prior to battery assembly, that is, prior tocombining the anode with a cathode in a battery cell.

In some embodiments, lithium metal (or some other lithiation material)is deposited onto the metal oxide layer prior to depositing thecontinuous porous lithium storage layer. The lithium may be deposited,for example, by evaporation, e-beam or sputtering. Some of the lithiummay form lithium oxide. In embodiments where the metal oxide layerincludes an oxide of a transition metal, e.g., copper or nickel, a mixedmetal oxide may form. In some embodiments, deposition of a lithium layerover the metal oxide may lessen first cycle losses in lithium duringelectrochemical formation (discussed below) of the anode.

In some embodiments, the ratio of deposited lithium metal atoms tooxygen atoms in the metal oxide layer is at least 0.02, alternatively inrange from 0.05 to 1.0. In some cases, the amount of deposited lithiummetal corresponds to at least 1% of the maximum lithium areal capacityof the continuous porous lithium storage layer, alternatively in a rangeof 2% to 10%, alternatively 10% to 30%, alternatively 30% to 50% or anycombination of these ranges.

In some embodiments, the continuous porous lithium storage layer may beat least partially prelithiated prior to a first electrochemical cycleafter battery assembly, or alternatively prior to battery assembly. Thatis, some lithium may be incorporated into the continuous porous lithiumstorage layer to form a lithiated storage layer even prior to a firstbattery cycle. In some embodiments, the lithiated storage layer maybreak into smaller structures, including but not limited to platelets,that remain electrochemically active and continue to reversibly storelithium. Note that “lithiated storage layer” simply means that at leastsome of the potential storage capacity of the lithium storage layer isfilled, but not necessarily all. In some embodiments, the lithiatedstorage layer may include lithium in a range of 1% to 10% of thetheoretical lithium storage capacity of the continuous porous lithiumstorage layer, alternatively 10% to 20%, alternatively, 20% to 30%,alternatively 30% to 40%, alternatively 40% to 50%, alternatively 50% to60%, alternatively 60% to 70%, alternatively 70% to 80%, alternatively80% to 90%, alternatively 90% to 100%, or any combination of contiguousranges thereof. In some embodiments, the metal oxide layer may capturesome of the lithium, and one may need to account for such capture toachieve the desired lithium range in the lithiated storage layer.

In some embodiments prelithiation may include depositing lithium metalover the continuous porous lithium storage layer, alternatively betweenone or more lithium storage sublayers, or both, e.g., by evaporation,e-beam or sputtering. Alternatively, prelithiation may includecontacting the anode with a reductive lithium organic compound, e.g.,lithium naphthalene, n-butyllithium or the like. In some embodiments,prelithiation may include incorporating lithium by electrochemicalreduction of lithium ion in prelithiation solution.

In some embodiments, one or more supplemental layers (described above)may be formed on the continuous porous lithium storage layer prior toprelithiation. The supplemental layer(s) may be used to control the rateof lithium incorporation. Non-limiting examples of the supplementallayer materials include silicon nitride, a metal oxide, a metal nitride,or a metal oxynitride.

In some embodiments, prelithiation includes physical contact of thecontinuous porous lithium storage layer with a lithiation material. Thelithiation material may include a reducing lithium compound, lithiummetal or a stabilized lithium metal powder, any of which may optionallybe provided as a coating on a lithium transfer substrate. The lithiumtransfer substrate may include a metal (e.g., as a foil), a polymer, aceramic, or some combination of such materials, optionally in amultilayer format. In some embodiments, such lithiation material may beprovided on at least one side of a current separator that faces theanode, i.e., the current separator also acts as a lithium transfersubstrate. Stabilized lithium metal powders (“SLMP”) typically have aphosphate, carbonate or other coating over the lithium metal particles,e.g. as described in U.S. Pat. Nos. 8,377,236, 6,911,280, 5,567,474,5,776,369, and 5,976,403, the entire contents of which are incorporatedherein by reference. In some embodiments SLMPs may require physicalpressure to break the coating and allow incorporation of the lithiuminto the continuous porous lithium storage layer. In some embodiments,other lithiation materials may be applied with pressure and/or heat topromote lithium transfer into the continuous lithium storage layer,optionally through one or more supplemental layers. In some embodimentsa pressure applied between an anode and a lithiation material may be atleast 200 kPa, alternatively at least 1000 kPa, alternatively at least5000 kPa. Pressure may be applied, for example, by calendering,pressurized plates, or in the case of a lithiation material coating on acurrent separator, by assembly into battery having confinement or otherpressurizing features.

In some embodiments, prelithiation includes thermally treating thecontinuous porous lithium storage layer during lithium incorporation,after lithium incorporation, or both during and after. The thermaltreatment may assist in the incorporation of the lithium into thecontinuous porous lithium storage layer, for example by promotinglithium diffusion. In some embodiments, thermally treating includesexposing the anode to a temperature in a range of 50° C. to 100° C.,alternatively 100° C. to 150° C., alternatively 150° C. to 200° C.,alternatively 200° C. to 250° C., alternatively 250° C. to 300° C., oralternatively 300° C. to 350° C. In some embodiments, thermal treatmentmay be done under controlled atmosphere, e.g., under vacuum or argonatmosphere to avoid unwanted reactions with oxygen, nitrogen, water orother reactive gases.

In some embodiments, prelithiation may soften the continuous porouslithium storage layer, for example, due to the formation of alithium-silicon alloy. This softening may cause problems in someprocesses, for example, roll-to-roll processes whereby the softenedlithium storage layer begins to stick to rollers or to itself duringwinding. In some embodiments providing at one or more supplementallayers prior to prelithiation or after prelithiation, the structuralintegrity and processability of the anode may be substantially improved.In some embodiments, the supplemental layer(s) may act as a harderinterface with other surfaces to prevent or reduce contact of suchsurfaces with the softened lithium storage material.

In some embodiments, lithium metal may be deposited over the continuousporous lithium storage layer followed by deposition of lithiumion-conducting layer. The anode may be thermally treated prior todeposition of the lithium ion-conducting layer, after deposition of thelithium ion-conducting layer, or both. In some embodiments, the lithiummetal is deposited directly onto the continuous porous lithium storagelayer. In some embodiments, a supplemental layer, e.g., silicon nitride,is deposited onto the continuous porous lithium storage layer prior todeposition of the lithium metal. In some embodiments, the lithiumion-conducting layer may include a lithium-containing material, a metaloxide, or a metalcone. Some non-limiting examples of lithiumion-conducting layer materials include a lithium phosphorous oxynitride(LIPON), a lithium phosphate, a lithium aluminum oxide, a lithiumlanthanum titanate, and alucones. The lithium ion-conducting layer mayinclude multiple sublayers of different materials, e.g., selected fromthe above list.

In some embodiments, the anode may be treated with a reducing agentprior to final battery assembly. The reducing agent may have anelectrochemical potential sufficient to reduce at least a portion of themetal oxide layer. The reducing agent may include an inorganic hydride,a substituted or unsubstituted borohydride, an amine-borane, or ananionic organic aromatic compound. In some embodiments, the reducingagent may be provided in a non-aqueous solvent that is itself notreduced by the reducing agent and applied under controlled conditionshaving low oxygen and moisture.

Thermal treatments were discussed above with respect to pre-lithiationand metal oxide precursors, but in some embodiments the anode may bethermally treated prior to battery assembly (after deposition of thecontinuous porous lithium storage layer is complete, but before theanode is combined with a cathode in a battery cell), with or without apre-lithiation step. In some embodiments, thermally treating the anodemay improve adhesion of the various layers or electrical conductivity,e.g., by inducing migration of metal from the current collector (i.e.,the metal oxide layer or the underlying electrically conductive metallayer) or atoms from the optional supplemental layer into the continuousporous lithium storage layer. In some embodiments, thermally treatingthe anode may be done in a controlled environment, e.g., under vacuum,argon, or nitrogen having a low oxygen and water content (e.g., lessthan 100 ppm or partial pressure of less than 10 Torr, alternativelyless than 1 Torr, alternatively less than 0.1 Torr to preventdegradation). Herein, “under vacuum” generally refers to a reducedpressure condition wherein the total pressure of all gasses (e.g. in avacuum oven) is less than 10 Torr. Due to equipment limitations, thevacuum pressure is typically greater than about 10⁻⁸ Torr. In someembodiments, anode thermal treatment may be carried out using an oven, atube furnace, infrared heating elements, contact with a hot surface(e.g. a hot plate), or exposure to a flash lamp. The anode thermaltreatment temperature and time depend on the materials of the anode. Insome embodiments, anode thermal treatment includes heating the anode toa temperature of at least 50° C., optionally in a range of 50° C. to600° C., alternatively 100° C. to 250° C., alternatively 250° C. to 350°C., alternatively 350° C. to 450° C., alternatively 450° C. to 600° C.,alternatively 600° C. to 700° C., alternatively 700° C. to 800° C., orany combination of contiguous ranges thereof. In some embodiments, theanode thermal treatment time may be in a range of about 0.1 min to about1 min, alternatively about 1 min to about 5 mins, alternatively about 5mins to about 10 mins, alternatively about 10 mins to about 30 minutes,alternatively about 30 mins to about 60 mins, alternatively about 60mins to about 90 mins, alternatively in a range of about 90 mins toabout 120 mins, or any combination of contiguous ranges thereof.

As illustrated in FIG. 8 , there are numerous process flow options forfabricating batteries incorporating anodes of the present disclosure.All of the steps of FIG. 8 have been discussed in more detail above andFIG. 8 is not an exhaustive list of all possibilities. In someembodiments, at least Steps 801, 805 and 817 are followed. In Step 801,a metal oxide layer is formed on an electrically conductive layer, e.g.,an electrically conductive metal layer such as a metal foil or metalmesh. In Step 805, one or more continuous porous lithium storage layersare deposited over or onto the metal oxide layer. In an alternativeembodiment, prior to step 805, lithium metal (or some other lithiationmaterial) may be deposited onto the metal oxide layer as shown in Step803. In some cases, the anode formed in Step 805 may be ready forassembly into a battery, Step 817.

In some embodiments, after Step 805, a prelithiation step may beincluded, e.g., Step 807 where lithium metal may be deposited onto thecontinuous porous lithium storage layer(s). In some cases, the anodefrom Step 807 may be ready to be assembled into a battery, Step 817. Inother embodiments as shown in Step 811, one or more lithiumion-conducting layer(s) may be deposited onto the product of Step 807prior to battery assembly Step 817.

In some embodiments, after Step 805, one or more supplemental layers maybe deposited onto the continuous porous lithium storage layer(s), asshown in Step 809. In some cases, the anode from Step 809 may be readyfor assembly into a battery, Step 817. In other embodiments, aprelithiation step may be included, e.g. as shown in Step 813 wherelithium metal may be deposited over or onto the supplemental layer(s).In some cases, the anode from Step 813 may be ready for assembly into abattery, Step 817. In other embodiments, one or more lithiumion-conducting layer(s) may be deposited onto the product of Step 813prior to battery assembly Step 817.

In addition to the explicit steps shown in FIG. 8 , thermal treatmentsor other treatments may be performed between any of the steps. Further,as mentioned, additional lithium storage layers that are not continuousporous lithium storage layers may be coated after Step 805. In someembodiments one or more steps may be performed using roll-to-rollcoating methods wherein the electrically conductive layer is in the formof a rolled film, e.g., a roll of metal foil.

In some cases, as shown in schematic FIG. 9A, the roll-to-rollprocessing may performed within a particular step wherein the apparatus901 for such step includes the necessary processing hardware 903, e.g.,for depositing, forming or treating a layer, along with a loading tool905 for holding a roll of film 906 to be processed, and a winding tool907 to roll up the processed film 908 after the step is complete. Tocarry out the next step, the processed roll may be transferred toprocessing apparatus 911, having its own processing hardware 913,loading tool 915, and winding tool 917. During transfer, the rolls maybe kept in a controlled environment, e.g., low oxygen or moisture,depending on the step.

In some cases, the roll-to-roll processing may include transfer of thefilm processed in one step directly to the next step or apparatus asshown schematically in FIG. 9B. Processing apparatus 921 is analogous toapparatus 901, but without the winding tool. Apparatus 921 includesloading tool 925 for holding the roll of film 926 to be processed andappropriate processing hardware 923, e.g., for depositing, forming ortreating a layer. The processed film 928 from the first step moves toprocessing apparatus 931 to receive another process step. Apparatus 931includes the appropriate processing hardware 933, e.g., for depositing,forming or treating a layer, and a winding tool 937 to roll up theprocessed film 938 after the next step is complete. Not shown, theprocessed film 938 may instead move to yet another processing apparatuswithout winding. Also, while drawn as separate units, in someembodiments apparatus 921 and apparatus 931 may share a common chamber.In some embodiments, a transition chamber or zone may be providedbetween apparatus 921 and 931 designed to avoid contamination of oneprocess with another, or to act as a film transport speed buffer if oneprocess requires less time than another.

Various combinations of the above embodiments may be employed together,depending on the compatibility of one apparatus interfacing withanother. Fabrication equipment may further include slitting stations.

Battery Features

The preceding description relates primarily to the anode (negativeelectrode) of a lithium-ion battery (LIB). The LIB typically includes acathode (positive electrode), an electrolyte and a separator (if notusing a solid-state electrolyte). As is well known, batteries can beformed into multilayer stacks of anodes and cathodes with an interveningseparator. Alternatively, a single anode/cathode stack can be formedinto a so-called jellyroll. Such structures are provided into anappropriate housing having desired electrical contacts.

In some embodiments, the battery may be constructed with confinementfeatures to limit expansion of the battery, e.g., as described in USpublished applications 2018/0145367 and 2018/0166735, the entirecontents of which are incorporated herein by reference for all purposes.In some embodiments a physical pressure is applied between the anode andcathode, e.g., using a tensioned spring or clip, a compressible film orthe like. Confinement, pressure, or both confinement and pressure mayhelp ensure that the anode remains in active contact with the currentcollector during formation and cycling, which may cause expansion andcontraction of the continuous porous lithium storage layer. In someembodiments, a jelly-roll battery design using metallic or other hardcylindrical housings may provide effective confinement, pressure, orboth confinement and pressure.

FIG. 10 is a schematic cross-sectional view of a battery according tosome embodiments of the present disclosure. Battery 790 includes topplate 760, bottom plate 762, anode side plate 764 and cathode side plate766, which form part of a housing for the stack of anodes 700, cathodes740 and intervening separators 730. Anodes are attached to an anode bus720 which is connected to anode lead 722 that extends through anode sideplate 764. Cathodes are attached to a cathode bus 750 which is connectedto cathode lead 752 that extends through cathode side plate 766. Battery790 further includes electrolyte 780 which fills the space and saturatesthe separators 730. Top compression member 770 and lower compressionmember 772 apply physical pressure (arrows) between the anodes andcathodes. Compression members may be compressible films, e.g., made froma porous polymer or silicone. Alternatively, compression members mayinclude an array of compressible features, e.g., made from porouspolymer or silicone. Alternatively, the compression members may includesprings or an array of springs. Alternatively, compression members maycorrespond to two sides of a compression clip or clamp. In someembodiments, the separator may act as a compressible film. In someembodiments the top and bottom plates may be formed a material and/orstructured to resist deformation thereby confining battery swell.

Cathode

Positive electrode (cathode) materials include, but are not limited to,lithium metal oxides or compounds (e.g., LiCoO₂, LiFePO₄, LiMnO₂,LiNiO₂, LiMn₂O₄, LiCoPO₄, LiNi_(x)Co_(y)Mn_(z)O₂, LiNi_(X)Co_(Y)AlzO₂,LiFe₂(SO₄)₃, or Li₂FeSiO₄), carbon fluoride, metal fluorides such asiron fluoride (FeF₃), metal oxide, sulfur, selenium, sulfur-selenium andcombinations thereof. Cathode active materials are typically providedon, or in electrical communication with, an electrically conductivecathode current collector.

In some embodiments, a prelithiated anode of the present disclosure isused with cathode including sulfur, selenium, or both sulfur andselenium (collectively referred to herein as “chalcogen cathodes”). Insome embodiments, a prelithiated anode of the present disclosure may bepaired with a chalcogen cathode having an active material layer, whereinthe active material layer may include a carbon material and a compoundselected selected from the group consisting of Se, Se_(y)S_(x),Te_(y)S_(x), Te_(z)Se_(y)S_(x), and combinations thereof, where x, y andz are any value between 0 and 1, the sum of y and x being 1, and the sumof z, y and x being 1, the compound impregnated in the carbon material,e.g., as described in US published application 2019/0097275, which isincorporated by reference herein for all purposes. The compound may bepresent in an amount of 9-90% by weight based on the total weight of theactive material layer. In some embodiments, the chalcogen cathode activematerial layer further includes conductive carbon nanotubes to improveoverall conductivity and physical durability and may permit fastercharging and discharging. The presence of carbon nanotubes may furtherallow thicker coatings that have greater flexibility thereby allowinghigher capacity.

Chalcogen cathodes are generally paired with lithium metal anodes.However, lithium metal anodes are difficult to handle, prone todegradation, and may further allow formation of dangerous dendriticlithium that can lead to catastrophic shorts. In some embodiments,prelithiated anodes of the present disclosure can achieve equivalentenergy storage capacity of a pure lithium anode, but are much easier tohandle and less prone to form dendritic lithium, thus making them morecompatible with chalcogen cathodes.

Current Separator

The current separator allows ions to flow between the anode and cathodebut prevents direct electrical contact. Such separators are typicallyporous sheets. Non-aqueous lithium-ion separators are single layer ormultilayer polymer sheets, typically made of polyolefins, especially forsmall batteries. Most commonly, these are based on polyethylene orpolypropylene, but polyethylene terephthalate (PET) and polyvinylidenefluoride (PVDF) can also be used. For example, a separator can have >30%porosity, low ionic resistivity, a thickness of ˜10 to 50 μm and highbulk puncture strengths. Separators may alternatively include glassmaterials, ceramic materials, a ceramic material embedded in a polymer,a polymer coated with a ceramic, or some other composite or multilayerstructure, e.g., to provide higher mechanical and thermal stability. Asmentioned, the separator may include a lithiation material such aslithium metal, a reducing lithium compound, or an SLMP material coatedat least on the side facing the anode.

Electrolyte

The electrolyte in lithium ion cells may be a liquid, a solid, or a gel.A typical liquid electrolyte comprises one or more solvents and one ormore salts, at least one of which includes lithium. During the first fewcharge cycles (sometimes referred to as formation cycles), the organicsolvent and/or the electrolyte may partially decompose on the negativeelectrode surface to form an SEI (Solid-Electrolyte-Interphase) layer.The SEI is generally electrically insulating but ionically conductive,thereby allowing lithium ions to pass through. The SEI may lessendecomposition of the electrolyte in the later charging cycles.

Some non-limiting examples of non-aqueous solvents suitable for somelithium ion cells include the following: cyclic carbonates (e.g.,ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylenecarbonate (PC), butylene carbonate (BC) and vinylethylene carbonate(VEC)), vinylene carbonate (VC), lactones (e.g., gamma-butyrolactone(GBL), gamma-valerolactone (GVL) and alpha-angelica lactone (AGL)),linear carbonates (e.g., dimethyl carbonate (DMC), methyl ethylcarbonate (MEC, also commonly abbreviated EMC), diethyl carbonate (DEC),methyl propyl carbonate (MPC), dipropyl carbonate (DPC), methyl butylcarbonate (NBC) and dibutyl carbonate (DBC)), ethers (e.g.,tetrahydrofuran (THF), 2-methyltetrahydrofuran, 1,4-dioxane,1,2-dimethoxyethane (DME), 1,2-diethoxyethane and 1,2-dibutoxyethane),nitriles (e.g., acetonitrile and adiponitrile) linear esters (e.g.,methyl propionate, methyl pivalate, butyl pivalate and octyl pivalate),amides (e.g., dimethyl formamide), organic phosphates (e.g., trimethylphosphate and trioctyl phosphate), organic compounds containing an S═Ogroup (e.g., dimethyl sulfone and divinyl sulfone), and combinationsthereof.

Non-aqueous liquid solvents can be employed in combination. Examples ofthese combinations include combinations of cyclic carbonate-linearcarbonate, cyclic carbonate-lactone, cyclic carbonate-lactone-linearcarbonate, cyclic carbonate-linear carbonate-lactone, cycliccarbonate-linear carbonate-ether, and cyclic carbonate-linearcarbonate-linear ester. In some embodiments, a cyclic carbonate may becombined with a linear ester. Moreover, a cyclic carbonate may becombined with a lactone and a linear ester. In some embodiments, theweight ratio, or alternatively the volume ratio, of a cyclic carbonateto a linear ester is in a range of 1:9 to 10:1, alternatively 2:8 to 7:3

A salt for liquid electrolytes may include one or more of the followingnon-limiting examples: LiPF₆, LiBF₄, LiClO₄, LiAsF₆, LiN(CF₃SO₂)₂,LiN(C₂F₅S₀₂)₂, LiCF₃SO₃, LiC(CF₃SO₂)₃, LiPF₄(CF₃)₂, LiPF₃(C₂F₅)₃,LiPF₃(CF₃)₃, LiPF₃ (iso-C₃F₇)₃, LiPF₅(iso-C₃F₇), lithium salts havingcyclic alkyl groups (e.g., (CF₂)₂(SO₂)_(2x)Li and (CF₂)₃(SO₂)_(2x)Li),and combinations thereof. Common combinations include: LiPF₆ and LiBF₄;LiPF₆ and LiN(CF₃SO₂)₂; and LiBF₄ and LiN(CF₃SO₂)₂.

In some embodiments, the total concentration of salt in a liquidnon-aqueous solvent (or combination of solvents) is at least 0.3 M,alternatively at least 0.7M. The upper concentration limit may be drivenby a solubility limit and operational temperature range. In someembodiments, the concentration of salt is no greater than about 2.5 M,alternatively no more than about 1.5 M.

In some embodiments, the battery electrolyte includes a non-aqueousionic liquid and a lithium salt.

A solid electrolyte may be used without the separator because it servesas the separator itself. It is electrically insulating, ionicallyconductive, and electrochemically stable. In the solid electrolyteconfiguration, a lithium containing salt, which could be the same as forthe liquid electrolyte cells described above, is employed but ratherthan being dissolved in an organic solvent, it is held in a solidpolymer composite. Examples of solid polymer electrolytes may beionically conductive polymers prepared from monomers containing atomshaving lone pairs of electrons available for the lithium ions ofelectrolyte salts to attach to and move between during conduction, suchas polyvinylidene fluoride (PVDF) or chloride or copolymer of theirderivatives, poly(chlorotrifluoroethylene),poly(ethylene-chlorotrifluoro-ethylene), or poly(fluorinatedethylene-propylene), polyethylene oxide (PEO) and oxymethylene linkedPEO, PEO-PPO-PEO crosslinked with trifunctional urethane,poly(bis(methoxy-ethoxy-ethoxide))-phosphazene (MEEP), triol-type PEOcrosslinked with difunctional urethane,poly((oligo)oxyethylene)methacrylate-co-alkali metal methacrylate,polyacrylonitrile (PAN), polymethylmethacrylate (PMMA),polymethylacrylonitrile (PMAN), polysiloxanes and their copolymers andderivatives, acrylate-based polymer, other similar solvent-freepolymers, combinations of the foregoing polymers either condensed orcross-linked to form a different polymer, and physical mixtures of anyof the foregoing polymers. Other less conductive polymers that may beused in combination with the above polymers to improve the strength ofthin laminates include: polyester (PET), polypropylene (PP),polyethylene naphthalate (PEN), polyvinylidene fluoride (PVDF),polycarbonate (PC), polyphenylene sulfide (PPS), andpolytetrafluoroethylene (PTFE). Such solid polymer electrolytes mayfurther include a small amount of organic solvents listed above. Thepolymer electrolyte may be an ionic liquid polymer. Such polymer-basedelectrolytes can be coated using any number of conventional methods suchas curtain coating, slot coating, spin coating, inkjet coating, spraycoating or other suitable method.

Additives may be included in the electrolyte to serve various functions.For example, additives such as polymerizable compounds having anunsaturated double bond may be added to stabilize or modify the SEI.Certain amines or borate compounds can act as cathode protection agents.Lewis acids can be added to stabilize fluorine-containing anion such asPF₆ ⁻. Safety protection agents include those to protect overcharge,e.g., anisoles, or act as fire retardants, e.g., alkyl phosphates.

In some embodiments, a solid-state electrolyte may be vapor deposited,solution-coated, melt-coated, or a combination thereof. Whether vapordeposited or coated from a solution or melt, embodiments of the presentdisclosure are advantageous over nanostructured devices. In the case ofvapor deposited solid-state electrolytes, anodes of the presentdisclosure do not have the problem of physical “shadowing” that nano- ormicro-structured devices do. Shadowing will create non-uniformdeposition of the electrolyte. The anodes disclosed here generally donot have high aspect ratio structures as described above, resulting inno or low shadowing effects. Vapor deposited solid electrolytes can bedeposited uniformly and rapidly over anodes of the present disclosurewithout resorting to slow atomic layer or other conformal coatingmethods. In the case of solution or melt-deposited solid-stateelectrolytes, anodes of the present disclosure may be more robust to thestresses and shear forces caused by the coating operation. High aspectratio nano- or micro-structures are susceptible to breakage from suchforces.

In some embodiments, the original, non-cycled anode may undergostructural or chemical changes during electrochemicalcharging/discharging, for example, from normal battery usage or from anearlier “electrochemical formation step”. As is known in the art, anelectrochemical formation step is commonly used to form an initial SEIlayer and involves relatively gentle conditions of low current andlimited voltages. The modified anode prepared in part from suchelectrochemical charging/discharging cycles may still have excellentperformance properties, despite such structural and/or chemical changesrelative to the original, non-cycled anode.

EXAMPLES

For Anodes 1-10, current collectors having a metal oxide layer (a nickeloxide) over an electrically conductive metal layer (nickel) wereprepared by placing nickel foil in a muffle furnace (heated air) andholding the foil at 700° C. for 30 minutes then cooled to roomtemperature. The metal oxide thickness was approximately 0.7 to 1.2microns.

Anode 1 (No Supplemental Layer)

The current collector was placed in a high-density plasma-enhancedchemical vapor deposition tool (HDPECVD) using silane gas as the sourceof silicon and argon carrier gas. Amorphous silicon was deposited overone side of the nickel foil at a total loading of about 0.8 mg/cm2 toform the continuous porous lithium storage layer having a thickness ofabout 4 μm.

Anode 2 (Si₃N₄ Supplemental Layer)

Anode 2 was prepared in the same way as Anode 1, but prior to removalfrom the HDPECVD tool, a nitrogen source was added to the silane/Ar gasmixture and 30 nm of substantially stoichiometric silicon nitride wasdeposited to form a supplemental layer over the continuous porouslithium storage layer (a-Si).

Anode 3 (Si₃N₄/TiO₂ Supplemental Layers)

Anode 3 was prepared in the same way as Anode 1, but prior to removalfrom the HDPECVD tool, a nitrogen source was added to the silane/Ar gasmixture and 15 nm of substantially stoichiometric silicon nitride wasdeposited to form a first supplemental layer over the continuous porouslithium storage layer (a-Si). The anode was transferred to an ALD tooland 6 nm titanium dioxide was deposited over the first supplementallayer to form a second supplemental layer.

Half Cells

Half cells were constructed using a 1.27 cm diameter punch of eachanode. Lithium metal served as the counter electrode which was separatedfrom the test anode using Celgard™ separators. The electrolyte solutionincluded: a) 88 wt. % of 1.0 M LiPF₆ in 3:7 EC:EMC (weight ratio); b) 10wt. % FEC; and c) 2 wt. % VC. Anodes first underwent an electrochemicalformation step. As is known in the art, the electrochemical formationstep is used to form an initial SEI layer. Relatively gentle conditionsof low current and/or limited voltages may be used to ensure that theanode is not overly stressed. For example, electrochemical formation mayinclude several cycles at low C-rates ranging from C/20 to C/5. Whilesilicon has a theoretical charge capacity of about 3600 mAh/g when usedin lithium-ion batteries, it has been found that cycle lifesignificantly improves if only a portion of the full capacity is used.Unless otherwise noted, the performance cycling was set to use about athird of the total capacity, i.e., about 1200 mAh/g (“capacity rating”).Unless otherwise notes, the performance cycling protocol generallyincluded 3 C charging and C/3 discharging to roughly a 20% state ofcharge. A 10-minute rest was provided between charging and dischargingcycles.

Plots of discharge capacity as a function of cycle # are shown in FIG.11 . All anodes have good cycle life even under these aggressivecharging conditions (3C). Anode 1 lasted about 300 cycles before showingsigns of decay. Adding a supplemental layer extended cycle life of Anode2 to about 400 cycles before signs of decay (an increase of −30%), withonly a minor loss of overall starting capacity (about 10%). Further,when it occurs, the rate of decay was substantially lower than Anode 1.Adding first and second supplemental layers extended the cycle life ofAnode 3 to almost 500 cycles before signs of decay (an increase of −60%over Anode 1) with an even smaller loss of overall capacity (about 5%).Further, when it occurs, the rate of decay was substantially lower thanAnode 1. Cycle life in terms of cycles to 80% of initial charge capacityfor Anodes 1-3 are tabulated below in Table 1 along with other anodes.

Additional anodes were prepared and tested in half cells in a mannersimilar to that described above.

Anode 4 (No Supplemental Layer)

Anode 4 was substantially the same as Anode 1. The continuous porouslithium storage layer included amorphous silicon having a thickness ofabout 4 μm and a density in range of about 1.8 to 2.0 g/cm3.

Anode 5 (Si₃N₄/Al₂O₃Supplemental Layers)

Anode 5 was substantially the same as Anode 4, but prior to removal fromthe HDPECVD tool, a nitrogen source was added to the silane/Ar gasmixture and 15 nm of substantially stoichiometric silicon nitride wasdeposited to form a first supplemental layer over the continuous porouslithium storage layer (a-Si). The anode was transferred to an ALD tooland 6 nm of aluminum oxide was deposited over the silicon nitride. Insubsequent testing below, this cell did not survive electrochemicalformation step. Thus, in some embodiments, when using a firstsupplemental layer of silicon nitride, it may be preferred not to usealuminum oxide as the second supplemental layer. Surprisingly, aluminumoxide performs poorly, and titanium dioxide appears to be a bettersecond supplemental layer in this case.

Anode 6 (TiO₂/Al₂O₃Supplemental Layers)

Anode 6 was similar to Anode 4 except that multiple supplemental layerswere deposited by ALD. The first supplemental layer included 10 nmtitanium dioxide and the second supplemental layer included 4 nmaluminum oxide. As shown in Table 1 below, the cycle life issubstantially improved over Anode 4 without the supplemental layers.

Anode 7 (Al₂O₃/TiO₂ Supplemental Layers)

Anode 6 was similar to Anode 4 except that multiple supplemental layerswere deposited by ALD. The first supplemental layer included 10 nmaluminum oxide and the second supplemental layer included 4 nm titaniumdioxide. As shown in Table 1, the cycle life was acceptable, but not asgood as Anode 4 without a supplemental layer and much lower than Anode 5having the reverse supplemental layer structure. While there may beother reasons to use the structure of Anode 7, in some embodiments, whenusing multiple metal oxide supplemental layer, it may be preferred notto use aluminum oxide as the first supplemental layer. Surprisingly,aluminum oxide performs poorly, and titanium dioxide appears to be abetter first supplemental layer in this case.

Anode 8 (60 nm SiO₂ Supplemental Layer)

Anode 8 was similar to Anode 4, but prior to removal from the HDPECVDtool, oxygen gas was added to the silane/Ar gas mixture and 60 nm ofsubstantially stoichiometric silicon dioxide was deposited to form asupplemental layer over the continuous porous lithium storage layer(a-Si). As shown in Table 1, the silicon dioxide causes a reduction inareal charge capacity, but the cycle life can be substantially improved.By increasing the capacity rating to 1600 mAh/g, the areal chargecapacity can be recovered so that is similar to Anode 4, and cycle lifeis still extended.

Anode 9 (120 nm SiO₂ Supplemental Layer)

Anode 9 was similar to Anode 8, except that 120 nm of substantiallystoichiometric silicon dioxide was deposited. As shown in Table 1, thesilicon dioxide causes a reduction in areal charge capacity, but thecycle life can be substantially improved. By increasing the capacityrating to 1600 mAh/g, the areal charge capacity can be recovered so thatis similar to Anode 4, and cycle life is still extended.

Anode 10 (SiO_(x) Lithium Storage Sublayer)

Anode 10 was similar to Anode 4 but prior to removal from the HDPECVDtool, an oxygen gas was added to the gas mixture and about 250 nm ofsub-stoichiometric silicon oxide was deposited to form a lithium storagesublayer over the amorphous silicon. The stoichiometry of the SiO_(x)sublayer is not known with certainty, but the oxygen gas flow rate wasset to only about 12% of the rate used to make a substantiallystoichiometric silicon dioxide. The overall thickness and density of thecombined sublayers of a-Si and SiO_(x) was about 4.5 μm and 2.1 g/cm3,respectively As shown in Table 1, Anode 10 has improved cycle liferelative to Anode 4 not having the SiO_(x) sublayer. Note that the cyclelife in Table 1 is the average of two replicates.

TABLE 1 Various performance parameters of Anodes 1-10, all at 3Ccharging C/3 discharge Parameter Capacity Initial charge Cycles to Anoderating capacity 80% of initial # (mAh/g) (mAh/cm²) charge capacity 11197 0.83 347 2 1202 0.77 472 3 1201 0.79 580 4 1237 0.83 354 5 Failedelectrochemical formation 6 1214 0.76 498 7 1214 0.76 273 8 1228 0.65689 8 1573 0.83 583 9 1204 0.57 977 9 1584 0.76 616 10 1123 0.76 576

Anode 11

A different current collector was prepared for Anode 11. Specifically, a50 nm TiO₂ (metal oxide) layer was deposited by ALD onto an electricallyconductive commercial copper foil. Silicon was deposited onto the TiO₂using an Oxford Plasmalabs System 100 PECVD tool at about 300° C.operated for 50 minutes at an RF power of about 225 W. The depositiongas was a mixture of silane and argon with gas flow ratio of about 1 to11, respectively, along with a boron-containing dopant gas. No hydrogengas was used. An adherent boron-doped amorphous silicon film about 14 μmthick having a density of about 1.7 g/cm3 was deposited.

Anodes 11A-11E

After silicon deposition, samples of Anode 11 were transferred to a tubefurnace under argon and thermally treated for various times andtemperatures to form Anodes 11A-11E as shown in Table 2 below.

Anodes 11 and 11A-11E were tested in half cells as previously describedexcept, due to larger charge capacity, the cell punch size was reduced.At the end of the formation cycles, the full areal charge capacity wasmeasured electrochemically along with final formation cycle currentefficiency. These data are also found in Table 2.

TABLE 2 Anode thermal treatment time and temperature Full areal chargeCoulombic efficiency Time Temp capacity final formation cycle Anode(min) (° C.) (mAh/cm²) (%) 11 n/a n/a 6.0 99 11A 60 475 6.5 99 11B 15475 6.7 99 11C 120 475 6.9 99 11D 15 375 6.0 99 11E 15 575 6.5 99

Although all anodes have very high areal charge capacity, the date inTable 2 show that anode thermal treatments appear to unlock someadditional charge capacity when treated at 475° C. or 575° C. (about 8%to 15% more than Anode 11 without the thermal treatment). Suchimprovements are commercially significant in lithium ion batteries andcan be used to: increase the charge capacity of the cell; decrease theweight and/or volume of the cell while maintaining cell charge capacity;increase the cycle life by lowering the rated capacity while maintainingoverall cell charge capacity; or some combination.

The performance of Anodes 11 and 11A-11E under cycling conditions weretested as described previously, but at C/3, 1 C and 3.2 C charging (allwith C/3 discharge). The anodes were capacity-rated at about 1100 mAh/g.For C/3 and 1 C charging schedules, cells were cycled to a targetinitial areal charge capacity of 2.0 mAh/cm2. The high charge rate 3.2 Ctest is completed with a charging current of 3.2 C, with a total timelimit of 15 min. This is a common fast charging test performed in thetrade (see “Battery Test Manual for Electric Vehicles”, Jon P.Christophersen, June 2015, INL/EXT-15-34184 Revision 3, page 5) If thecell completes all of its charging galvanostatically, it will achieve3.2*0.25 or 80% of its rated capacity, which in this case is 1.6mAh/cm2. Cells that hit the charging voltage limit prior to 15 min, willcharge both galvanostatically and potentiostatically. The lattercharging portion will result in cells achieving less than 80% of theirrated capacity. None of these anodes have finished cycling or reachedtheir 80% of the initial charge capacity (except Anode 11A which did soat about 400 cycles), but plots are shown in FIG. 12 (C/3 charge), FIG.13 (1 C) and FIG. 14 (3.2 C). The test cells were not all started at thesame time, so they are at various stages of cycling.

Inspection of FIG. 12 shows that there is not yet any substantialdifference between the anodes at C/3 charging.

FIG. 13 reveals a dip in Anode 11 performance at cycles 25-60 relativeto all of the other anodes. It also appears that Anode 11 is showingsome cycle fading starting at about cycle 225. Of the two thermallytreated anodes that have reached at least 230 cycles at this writing(11A @ 276 cycles and 11B @ 237 cycles), no such fading has beenobserved. Thus, at faster charge rates than C/3, the thermally treatedanodes appear to show improved cycle life.

FIG. 14 shows that the non-thermally treated Anode 11 never reaches 80%state of charge at 3.2 C, i.e., instead of 1.6 mAh/cm2, Anode 11 onlyreaches about 1.25 mAh/cm2. Due to its more resistive properties, itdoes not complete 15 min. of galvanostatic charging. In contrast, thethermally treated anodes do hit 80% state of charge for at least a fewcycles; the fact that their capacities are closer to the 1.6 mAh/cm2limiting capacity indicates most of their charging remainsgalvanostatic. It is postulated that the combination of very fastcharging of 3.2 C in combination with the high-capacity silicon anode(relative to Anodes 1-10) may have resulted in some resistance in theflow of electrons or lithium diffusion. However, it is noted that all ofthe thermally treated samples, Anodes 11A-11E, were much closer to thetarget charge capacity than Anode 11, which did not have the thermaltreatment. Thus, it appears that anode thermal treatments may be used toimprove fast charging characteristics of the anode.

Despite the industry's advocacy of micro- or nanostructured silicon orother lithium storage materials, it has been found in the presentdisclosure that highly effective anodes can be formed without suchfeatures. Although the present anodes have been discussed with referenceto batteries, in some embodiments the present anodes may be used inhybrid capacitor devices. Relative to comparable micro- ornanostructured anodes, the anodes of the present disclosure may have oneor more of at least the following unexpected advantages: comparable orimproved stability at aggressive ≥1 C charging rates; higher overallareal charge capacity; higher gravimetric charge capacity; highervolumetric charge capacity; improved physical durability; simplifiedmanufacturing process; and/or a more reproducible manufacturing process.

Although the present anodes have been discussed with reference tobatteries, in some embodiments the present anodes may be used in hybridlithium ion capacitor devices. Some non-limiting representativeembodiments are listed below.

What is claimed is:
 1. An anode for an energy storage device comprising:a current collector comprising a metal oxide layer; a continuous porouslithium storage layer overlaying the metal oxide layer, wherein thecontinuous porous lithium storage layer is substantially free ofnanostructures and comprises amorphous silicon deposited by a PECVDprocess; and a first supplemental layer overlaying the continuous porouslithium storage layer, the first supplemental layer comprising siliconnitride, silicon dioxide, or silicon oxynitride.
 2. The anode of claim1, wherein the first supplemental layer comprises substantiallystoichiometric silicon nitride, and the first supplemental layer has athickness in a range of about 2 nm to about 50 nm.
 3. The anode of claim1, wherein the first supplemental layer comprises substantiallystoichiometric silicon dioxide, and the first supplemental layer has athickness in a range of about 10 nm to about 150 nm.
 4. The anode ofclaim 1, further comprising a second supplemental layer overlaying thefirst supplemental layer, wherein the second supplemental layer ischaracterized by a composition different than the first supplementallayer composition, and the second supplemental layer comprises silicondioxide, silicon nitride, silicon oxynitride, or a metal compound. 5.The anode of claim 4, wherein the metal compound comprises a metaloxide, metal nitride, or metal oxynitride, and wherein the secondsupplemental layer has a thickness in a range of about 2 nm to about 50nm.
 6. The anode of claim 4, wherein the first supplemental layercomprises substantially stoichiometric silicon nitride, and the secondsupplemental layer does not comprise aluminum oxide.
 7. The anode ofclaim 4, wherein the metal compound comprises a lithium-containingmaterial.
 8. The anode of claim 7, wherein the lithium-containingmaterial comprises a lithium phosphorous oxynitride, a lithiumphosphate, a lithium aluminum oxide, or a lithium lanthanum titanate. 9.The anode of claim 8, wherein the second supplemental layer has athickness in a range of about 5 nm to about 150 nm.
 10. The anode ofclaim 4, wherein the metal compound comprises a metalcone.
 11. The anodeof claim 4, further comprising one or more additional supplementallayers overlaying the first and second supplemental layers, wherein atleast one of the additional supplemental layers comprises a metal oxide,a metal nitride, a metal oxynitride, a lithium-containing material, or ametalcone.
 12. The anode of claim 1, wherein the continuous porouslithium storage layer comprises at least 85 atomic % amorphous silicon,and the continuous porous lithium storage layer has a density in a rangeof 1.1 g/cm3 to 2.2 g/cm3.
 13. The anode of claim 1, wherein the metaloxide layer comprises an oxide of nickel or an oxide of titanium and hasa thickness of at least 0.01 μm.
 14. The anode of claim 1, furthercomprising one or more additional supplemental layers overlaying thefirst and second supplemental layers, wherein at least one of theadditional supplemental layers comprises a metal oxide, a metal nitride,a metal oxynitride, a lithium-containing material, or a metalcone. 15.The anode of claim 1, wherein the continuous porous lithium storagelayer comprises a metal from the metal oxide layer in an atomic % rangeof 0.05% to 5%.
 16. The anode of claim 1, further comprising anelectrically conductive layer, and the metal oxide layer is interposedbetween the electrically conductive layer and the continuous porouslithium storage layer.
 17. The anode of claim 16, wherein theelectrically conductive layer comprises stainless steel, titanium,nickel, copper, a conductive carbon, or a combination thereof.
 18. Theanode of claim 17, wherein the continuous porous lithium storage layercomprises a metal from the electrically conductive layer in an atomic %range of 0.05% to 5%.
 19. The anode of claim 1, wherein the continuousporous lithium storage layer has a thickness of at least 3 μm.
 20. Theanode of claim 1, wherein the continuous porous lithium storage layerincludes less than 1% by weight of carbon-based binders.